The present invention relates to a shockwave source for use in and as a part of a lithotripter and includes an areal wave generator cooperating with a parabolic reflector.
U.S. Pat. No. 3,942,531 and others, e.g. 4,539,989; 4,570,634; 4,622,969; 4,662,375; 4,809,682 show pointlike sources for the generation of shockwaves in a lithotripter. Contrary to the technology which is included in the reference and others an areal shockwave source is shown in German printed patent application 31 19 295. The source as disclosed here is composed of a plurality of individual piezoceramic elements. They are arranged e.g. in a self focusing configuration i.e. they delineate as spherical calotte or they are arranged to cooperate with a reflector or a lens in order to obtain focusing of the areally produced shockwaves. The shockwave front can be produced through appropriate control which is feasible on account of the nonlinear propagation of a single sound wave provided, the intensity is sufficiently high.
German printed patent application 34 47 440 suggests a shockwave generator for the contactfree non-invasive lithotripsy which includes an areal wave generator which in this case is constructed as an electromagnetic shockwave pipe and cooperating with a parabolically shaped reflector. This reflector focuses the shockwave as it is produced in a planar configuration originally into the concrement to be comminuted in the body of a patient. Such kind of source is basically in the background of the invention alluded to above and which will be improved by detailed features of the invention.
In order to comminute concrements very efficiently in situ and in vivo with as few side and after effects of the treatment as possible, one can summarize the following essential technical requirements for the formation of a shockwave system. First of all the dynamics of the power is to have is to be very high; the device must provide for good focusing of, preferably, unipolar pulses with low pressure and particularly low tension produced as the wave reaches the body of the patient. It is necessary to locate on one hand the concrements through ultrasonic and/or X-rays with sufficient accuracy and to place the focus of the lithotripter into that location. A long use life is desirable and owing to the fact that often only very limited space is available in the immediate vicinity of the patient, the device should be of a compact construction.
In some form or another these demands are satisfied individually, but often not completely and as far as known to us they are not all satisfied in one piece of equipment, e.g. the pointlike source for shockwave energies as they are widely used in commercial application for kidney stone comminution, does provide a high power but the dynamic range is only limited to lower power levels. Moreover it was found that occasionally a supplemental, centrally (axially) positioned ultrasonic locating device may interfere with the comminuting device and vice versa.
Self focusing piezosystems are very large owing to the low local intensity in ultrasonic production. Planar electromagnetic coil systems do have adequate powder density in the source but it is difficult to obtain high aperture configuration for focusing with a lens system. Self focusing electromagnetic calotte system have unfortunately a very limited use life.